OBR: Ear

How many hillocks are there and which branchial arches do they arise from?

Six

1-3 arise from the first branchial arch

4-6 arise from the second branchial arch

What does each hillock of His become?

1 - tragus

2 - helical crus

3 - helix

4 - antihelix

5 - antitragus

6 - lobule and lower helix

How does a preauricular sinus tract form?

From improper fusion of the 1st and 2nd branchial arches

When does development of the external auditory canal (EAC) begin?

The canal begins to develop at 28 weeks gestation.

At what month(s) gestation does the ear canal open?

7th

At what age does the EAS reach adult size?

9 years

What is the significance of a congenitally malformed auricle?

The auricle develops early, making malformations of the middle ear, mastoid, and VII more likely.

What is the significance of a normal auricle with canal atresia?

The EAC begins formation late (28th week), so the middle ear and ossicles are more likely to be normal.

Which ossicles develop from the first branchial arch (Meckel's cartilage)?

Head and neck of the malleus

Body and short process of the incus

Which ossicles develop from the second branchial arch (Reichert's cartilage)?

Manubrium of the malleus

Long process of the incus

Stapes (except footplate)

What does the stapes footplate develop from?

Otic mesenchyme

Which ossicular component develops from membranous bone?

Anterior process of the malleus

Which ossicular components never completely ossify?

Part of the manubrium

The vestibular portion of the stapes footplate

When do the ossicles reach adult size and shape?

Adult size - at the 16th week gestation

Adult shaped - by birth

Why is the development of the bony otic capsule unique?

It is formed from 14 centers of ossification that fuse and leave no suture lines

The centers are formed from cartilage, but retain no areas of chondral growth

The bone retains its fetal character, with Haversian canals

When does the otic capsule begin formation?

The precursors of the otic capsule are present at 8 weeks

The ossification centers are present at 15 weeks

When does the otic capsule finish developing?

Reaches adult size by 21-24 weeks

What is the last part of the otic capsule to ossify?

Fissula ante fenestrum

When does the fallopian canal begin developing?

5th week gestation

Development is not complete until several years after birth

What is the last structure of the inner ear to develop?

Endolympatic sac

What does the eustachian tube (ET) develop from?

From the 1st pouch (between the 2nd arch and the pharynx)

Which branchial arch does the tensor tympani muscle arise from?

First branchial arch

True/False: The tympanic membrane is derived from ectoderm.

False; it is derived from ectoderm, mesoderm, and endoderm

At what age is the mastoid process completely pneumatized?

2yo

What is the sensory innervation of the auricle?

Greater auricular nerve (C3)

Auriculotemporal nerve (V3)

Lesser occipital nerve (C2,3)

Auricular branch of the vagus (Arnold's nerve)

Sensory branches of VII and IX

What is Arnold's nerve?

Auricular branch of the vagus that innervates skin of the external auditory canal and auricle

What is the foramen of Huschke?

An embryologic remnant that normally obliterates in the anteroinferior portion of the medial bony EAC

What is the clinical significance of the foramen of Huschke?

Serves as a potential route for spread of tumor from the parotid gland to the temporal bone.

Which wall of the EAC is shorter - the anteroinferior or posterosuperior?

Posteriosuperior - ~25mm (vs anteroinferior - ~31mm)

How much of the EAC is cartilaginous?

1/3

How much of the ET is cartilaginous?

2/3

Where is the tympanic notch of Rivinus?

Superior portion of the tympanic ring (squamous portion of the temporal bone)

How does the composition of gas in the middle ear differ from that of room air?

Lower oxygen level and higher carbon dioxide & nitrogen levels.

What are the layers of the tympanic membrane?

Squamous epithelium

Radiating fibrous layer

Circumferential fibrous layer

Mucosa

Which has greater sensory innervation - pars tensa or pars flaccida?

Pars flaccida

What are the three nerves of the tympanic plexus?

V3

IX (Jacobson's nerve)

X

Which part of the ossicular chain has the most tenuous blood supply and is most prone to necrosis?

Long process of the incus

Which part of the malleus articulates with the incus?

Head

Where in the ossicular chain does the tensor tympani muscle insert?

Manubrium of the malleus

Which part of the malleus does the anterior ligament attach to?

The neck, near the anterior process

What ligament supports the stapes?

Annular ligament

Where does most of the movement of the stapes occur?

Anterior-superior portion of the footplate

Where in the ossicular chain does the stapedius muscle insert?

Posterior neck of the stapes

What is the scutum?

Lateral wall of the epitympanum

What are the boundaries of the epitympanum?

Superiorly - the tegmen

Inferiorly - the fossa incudis

Anteriorly - the zygomatic arch

Posteriorly - the aditus

Medially - the lateral semicircular canal & VII

Laterally - the scutum

Which ossicles can be found in the epitympanic recess?

Head of the malleus

Body & short process of the incus

What is the inferior boundary of they tympanic cavity?

Jugular bulb

What structures are anterior to the tympanic cavity?

Carotid artery

ET

Canal for the tensor tympani muscle

What structures are posterior to the tympanic cavity?

Aditus

Posterior sinus

Chorda tympani

Fossa incudis

Pyramidal prominence

Stapedial tendon

What is the promontory?

Elevation of the medial wall of the tympanic cavity formed by the basal turn of the cochlea

Which 3 cranial nerves are found beneath the floor of the middle ear cavity?

IX - glossopharyngeal

X - vagus

XI - accessory

Below is a diagram of the right middle ear showing its relationship with the inner ear. Name the structures:

A - facial nerve

B - Ponticulus

C - Subiculum

D - Geniculate ganglion

What structure is located inferior to the subiculum and posteroinferior to the promontory?

Round window

What structure lies between the subiculum and the ponticulus?

Sinus tympani

What structure lies superior to the ponticulus?

Oval window

What structure lies between the prominence of SCC and the promontory/oval window?

Prominence of the facial canal

The following diagram is of a right middle ear viewed from below. Name the structures:

A - facial recess

B - facial nerve

C - Sinus tympani

What is the most anterior structure of the medial wall of the tympanic cavity?

Cochleariform process

Cochleariform process: tensor tympani:: pyramidal process: ?

Stapedius

What structure is situated just medial to the tip of the cochleariform process?

Geniculate ganglion of the facial nerve.

Between which ossicles does the chorda tympani run?

Manubrium of the malleus and the long process of the incus

What is the function of the chorda tympani nerve?

Parasympathetic innervation to the submandibular and sublingual glands

Taste to the anterior 2/3 of the tongue

Which planes are the oval and round windows oriented in?

Oval window is in the sagittal plane

Round window is in the transverse plane

What structure ends blindly at the round window?

Scala tympani (lower compartment of the cochlea)

What is the name of the central bony core of the cochlea through which nerves and vessels travel?

Modiolus

What is the name of the area of communication between the scala vestibuli and the scala tympani?

Helicotrema

What fluid surrounds the membranous labyrinth?

Perilymph

How does perilymph differ from endolymph?

Perilymph

pH 7.2

High in sodium

Low in potassium

Does not contain chloride

Endolymph

pH 7.5

Low in sodium

High in potassium and chloride

True/False: The membranous labyrinth is a self-contained system.

True.

What are the main structures of the vestibular portion of the membranous labyrinth?

Utricle

Saccule

SCCs

Which of the main structures of the vestibular portion of the membranous labyrinth receives the crura from the three SCCs?

Utricle

What structures house the crista?

Ampullae

What is the blood supply to the inner ear?

Labyrinthine artery

(branch of the anterior inferior cerebellar artery)

What structure produces endolymph?

Stria vascularis

Where does most of the resorption of endolymph occur?

Endolymphatic sac.

What does the vestibular aqueduct carry?

Endolymphatic duct

Accompanying vein

Where is the primary auditory cortex?

Brodmann's area 41 in the superficial portion of the temporal bone

Which part of the vestibular labyrinth detects angular acceleration?

SCCs

What do the utricle and saccule detect?

Linear acceleration

Where are cupula found?

SCCs

What 3 systems determine balance?

Vestibular

Vestibulo-ocular (visual)

Vestibulo-spinal (proprioceptive)

Which part of the cochlea represents high-frequency sounds?

The basal end

What range of frequencies can the human ear detect?

20 - 20,000 Hz

(the greatest sensitivity is from 500 - 3000 Hz)

What noise level begins to cause pain?

140 dB

How many times louder is 60 dB than 0 dB?

1,000,000 times

What are normal ear volumes in children and adults?

Children: 0.5 - 1.0 cm3

Adults: 0.6 - 2.0 cm3

Which cells omit otoacoustic emissions (OAEs)?

Outer hair cells

What percentage of normal ears emit spontaneous OAEs?

35 - 60%

What are the 4 parts of the temporal bone?

Squamous

Tympanic

Petrous

Masoid

What are the 4 openings into the temporal bone?

Internal Auditory Canal (IAC)

Vestibular aqueduct

Cochlear aqueduct

Subarcuate fossa

What is Hyrtl's fissure?

Connection between the subarachnoid space near the IX ganglion and the hypotympanum that allows middle ear infections to spread to the brain (normally closes with maturation)

What proportion of the population has a pneumatized petrous pyramid?

1/3

What is Trautmann's triangle?

Triangle between the external prominence of the lateral and posterior SCCs and the posterosuperior corner of the mastoid

What is Korner's septum?

AKA the "false bottom"

It represents the suture line between the petrous and squamous portions of the temporal bone

What is meant by a "diploic mastoid"?

Occupied by bone marrow instead of air cells

What structure forms the arcuate eminence?

Superior SCC

True/False: The position of the cochlear duct is always inferior to the lowest border of the stapes footplate.

True

Besides muscles of facial expression, what muscles does the facial nerve innervate?

Posterior belly of the digastric

Stylohyoid

Stapedius muscle

What does the facial nerve provide general sensation for?

Part of the auricular concha

External auditory canal

Tympanic membrane

What is the function of the special visceral afferent fibers of the facial nerve?

To provide taste to the anterior 2/3 of the tongue and palate (via the chorda tympani)

Where are the cell bodies for the special visceral afferent fibers of the facial nerve?

Geniculate ganglion

What is the function of the nervus intermedius?

To carry visceral motor fibers to the lacrimal gland, minor salivary glands, and mucosal glands of the palate and nose (via the greater superficial petrosal nerve)

To carry general sensory fibers from the auricular concha and external auditory canal

What are the six segments of the facial nerve?

Intracranial

Internal auditory canal

Labyrinthine

Tympanic

Mastoid/vertical

Extratemporal

Where in the brainstem is the facial motor nucleus?

Caudal pons

Where does the facial nerve leave the brainstem?

Pontomedullary junction, close to the vestibulocochlear nerve

What are the limits of the tympanic segment of VII?

Geniculate ganglion to the 2nd genu (adjacent to the pyramidal process)

What are the limits of the mastoid segment of VII?

Pyramidal process to the stylomastoid foramen

Which segment of VII is the shortest?

Labyrinthine

Which segment of VII has the narrowest passageway?

Labyrinthine

What portion of the facial nerve is closest to the cochlea?

Labyrinthine

What 3 branches of the facial nerve are given off in its course through the temporal bone?

Greater superficial petrosal nerve

Nerve to the stapedius muscle

Chorda tympani

What is the first branch of the facial nerve?

Greater superficial petrosal nerve

Where along the course of the facial nerve does this nerve branch off?

Geniculate ganglion

What is the blood supply to the geniculate ganglion?

Greater superficial petrosal artery

(branch of the middle meningeal artery)

What is the function of the greater superficial petrosal nerve?

Lacrimation

Salivation from minor salivary glands

Mucosal secretions from nose and palate

Where do the preganglionic parasympathetic neurons of the greater superficial petrosal nerve synapse?

Pterygopalatine ganglion

Branches of which nerve then carry the postganglionic parasympathetic neurons to the mucus-secreting glands in the nose, sinuses, and palate?

Maxillary division of the trigeminal nerve

What is the facial hiatus?

Dehiscence of variable size in the petrous portion of the temporal bone in the floor of the middle cranial fossa, which marks the entrance of the greater superficial petrosal nerve into the middle cranial fossa

How is the facial hiatus clinically significant?

The geniculate ganglion usually lies deep to the hiatus but in 5-10% of patients, it lies under the dura within the hiatus and without a bony covering

Describe the path of the facial nerve in the temporal bone:

Enters the IAC --> travels laterally for a short distance --> just superior to the promontory it makes a sharp turn to run posteriorly (at the external/first genu and the geniculate ganglion) --> continues posteriorly with a slight inferolateral inclination (forming the prominence of the facial canal in the medial wall of tympanic cavity) --> behind the base of the pyramidal eminence the nerve makes a broad turn to descend vertically and somewhat laterally (2nd genu) through the mastoid cavity

What is the average diameter of the IAC?

6.8 mm

What is the upper limit of normal diameter of the IAC?

8 mm

What is the narrowest intratemporal portion of the fallopian canal?

Entrance to the fallopian canal at the lateral aspect of the IAC (fundus)

What structure bisects the IAC in the vertical direction and in the horizontal direction?

Bill's bar; transverse/falciform crest

Below is a cross-sectional diagram of the IAC. Name the structures:

A - facial nerve

B - Superior branch of the vestibular nerve

C - Cochlear nerve

D - Inferior branch of the vestibular nerve

What does the superior vestibular nerve innervate?

Superior and lateral SCCs

Utricle

Saccule

What does the inferior vestibular nerve innervate?

Posterior SCC

Macula of the saccule

Where is the 2nd genu of the facial nerve?

Just distal to the geniculate ganglion at the sinus tympani between the tympanic and mastoid segments

What is the relationship of the 2nd genu of the facial nerve to the lateral SCC and short process of the incus?

The 2nd genu is inferior to the lateral SCC and medial to the short process of the incus

In its tympanic segment, between which structures does the facial nerve travel?

Superiorly - the lateral SCC

Inferiorly - the oval window

Where does the facial nerve lie in relation to the cochleariform process?

Posterosuperior

What is the cog?

A ridge of bone that extends inferiorly from the tegmen epitympanum and partially separates the anterior epitympanic compartment from the mesoepitympanum

What is the relationship of the tympanic portion of VII to the cog?

VII lies anterior to the cog in the floor of the anterior epitympanum

What percentage of people have a dehiscence of the facial nerve in either the tympanic or mastoid segments?

50 - 55%

Where is the most common site of dehiscence?

Tympanic segment superior to the oval window

What is the last branch of the facial nerve before it passes through the stylomastoid foramen?

Chorda tympani

Where does the chorda tympani arise in relation to the stylomastoid foramen?

Usually 4-7mm superior

What artery accompanies the chorda tympani?

Posterior tympanic artery

What is the name of the opening through which the chorda tympani nerve enters the infratemporal fossa?

Petrotympanic fissure (canal of Huguier)

Where are the cell bodies of the motor fibers of the chorda tympani nerve?

Superior salivatory nucleus

What 3 motor branches does the facial nerve give off just after exiting the stylomastoid foramen?

Nerve to posterior belly of digastric

Nerve to the stylohyoid

Nerve to the postauricular muscle

Where is the facial nerve trunk located in relation to the tympanomastoid suture line?

6-8mm anteroinferior (between the suture line and the styloid process)

What is the name of the point at which the facial nerve divides into the upper and lower divisions?

pes anserinus

How far is the pes anserinus from the stylomastoid foramen?

~1.3 cm

How does facial nerve innervation to the upper face differ from that to the lower face?